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Re: WiSP, AO10 & FM sats

on 9/28/00 2:12 AM, Michael Hart at mhart@terrigal.net.au wrote:

> One of my biggest problems is trying to sort out real (wanted) signals from
> the muck.  I seem to get some "birdies" as I have said before.  I also get
> some intermodulation when I transmit.  This has thrown me a number of times.
> I though I was getting a real return from UO14 for over 30 minutes ;).  Then
> I turned the 70cm preamp off and it went away.

What you are doing is desensing your UHF RX with your two meter uplink.
Keep in mind that 432 is the thrid harmonic of 144 MHz.  Your preamp is a
very, very sensitive piece of equipment designed to pick up low signal
levels.  If your third harmonic off 2 meters is on the order of the same
signal level as a satellite signal (very likely is), you can easily pick it
up and amplify it into your RX.

Your best bet is to get some good filters for both bands.  Sure you have a
little more loss, but the preamp will fix that.  DCI makes great filters but
they are costly.  ICE makes some low power jobbies for 2m, but be careful!
They are rated at 150 Watts, but they WILL NOT handle 150 W CW!  They are
very low duty cycle!

I have a 2m DCI filter and on 432, I run the signal through a Larsen
duplexer.  A duplexer is just a filter with one input and two outputs with
separate passbands.  I just leave the VHF side disconnected.  It works well!

There are also "coffee can" filter examples in the handbooks.



Jon Ogden
NA9D (ex: KE9NA)



"A life lived in fear is a life half lived."

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